How do sunscreens work?

I know I’ve been pretty slack with the science posts (thesis writing makes me never want to read another science article again!), but I decided to do this one, because a few people have asked me about it recently. There’ll be a few sciencey DIY beauty projects soon though, hope that satisfies any nerdy cravings! :)

photo credit: mark sebastian

How do sunscreens work?

There are two main types of sunscreens: chemical and physical. Often a tube of sunscreen will contain a combination of the two.

Physical sunscreens work by blocking out, absorbing and scattering UV. They essentially work like a million little men standing on your skin holding umbrellas. Examples of physical sunscreens are zinc oxide and titanium dioxide – the “nano” sunscreens fall in this category.

Chemical sunscreens are a bit more complex. Some organic (meaning carbon-based, not pesticide-free!) chemicals can absorb UV light. The process is a bit complex to explain (it’s a barrel of fish containing pi electrons and discrete energy levels), but the result is that chemicals which have a double bond/single bond/double bond structure are able to absorb UV light and dissipate it as heat energy. Examples of chemical sunscreens include oxybenzone and ensulizole – as you can see, they have lots of double/single/double bond patterns which allow them to absorb UV light.

An analogy to how this works is when black objects absorb visible light and turn it into heat energy, which is why most people don’t wear black to the beach!


  1. says

    Thanks so much for the science post :) Hope you’re going okay with your thesis too – I have one last assignment due then I’ll be free from them all :D Can you tell I’m excited? ;)

    • says

      It’s going ok, a bit behind schedule but I’m not super stressed at the moment! Woohoo only one assignment left – I hated assignments! :) Then you have time for ALL THE POLISH!!

  2. says

    Great post michelle. I always wondered, sunscreen only stops from you from burning right? Or tanning as well? Because I always seem to get a tan, but then again I tan so easily, 5 mins and i’m done haha

    • says

      It depends on your skin really – people who tan easily (like you) don’t need much UV light to tan, so sunscreen could well let through enough for you to tan, since it doesn’t completely block all the UV radiation :) I tan easily too – I only need to go to the beach once in summer and I’m tanned until July. Once someone even asked me if I’d been to the Northern Hemisphere on holiday haha!

  3. says

    I do so enjoy these posts! Love your blog! I knew how the physical sunscreens work but had no clue about the chemical types! Thanks for the mini science lesson. =)

    • says

      Same!! I love these sciencey posts so much, because I love knowing how things work. I already knew about the physical ones, but never properly understood how the chemical sunscreens worked.
      So thanks!- Also, love the analogies, makes it so much easier to skim read and understand!!


    • says

      Thanks Michaela! I must admit I’m a bit of an analogy fiend – I’ve been known to draw little men playing tug-of-war on chemical bonds on the whiteboard while my first years look on in bemusement :

  4. says

    LOL thesis! I say this of course, because if you don’t laugh about it, all you can do is cry. I know your pain, 6th year grad student here, WAH!

    • says

      Oh no! Argh, as I’m sure you understand it’s pretty much the most stressful thing I’ve ever done. I finally understand why people say it’s kind of like childbirth….


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